Tissue kallikreins are a ubiquitous family of relatively specific serine proteases thought to be significant in the control of blood pressure and the maintenance of various renal functions. In vitro, kallikrein cleaves specific peptide bonds in kininogen, prorenin, plasminogen activating factor, atriopeptigen, and proinsulin to produce biologically active hormones and enzymes. In vivo, the actions of tissue kallikrein are poorly understood because of the lack of specific inhibitors. The objective of research proposed here is to continue the development of inhibitors of tissue kallikrein and, after appropriate characterization for specificity, apply these to clarify the function of the enzyme in vivo. The research proposed can be divided into the design and characterization of kallikrein inhibitors and in vivo testing. Three strategies will be used to prepare inhibitors. These include: (1) optimization of presently available competitive inhibitors based on the amino acid sequence of kininogen (substrate analogs), (2) design of inhibitors modeled on the reactive site of aprotinin and (3) development suicide inhibitors which irreversibly block the protease. The inhibitors will be characterized for both affinity and specificity. Specificity will be evaluated by testing representative inhibitors against tissue kallikreins isolated from various species, other purified proteolytic enzymes, isolated systems such as those involved in blood clotting and complement fixation and in vivo for non-specific blockade of the adrenergic, renin-angiotensin and other systems. In vivo testing of the kallikrein inhibitors will focus on the effect of the compounds on blood pressure, regional distribution of blood flow and changes in various kidney parameters.